(1) Field of the Invention
The invention is related to an airfoil for a rotor blade of a rotary wing aircraft, said airfoil having a predetermined maximum thickness to chord ratio. The invention is further related to a rotor blade of a rotary wing aircraft.
(2) Description of Related Art
Airfoils for rotor blades of rotary wing aircrafts are generally characterized by an extrados and an intrados that are arranged between corresponding leading and trailing edges of the airfoils and that are defined by predetermined intrados coordinate value pairs x/c, yint/c and predetermined extrados coordinate value pairs x/c, yext/c. Therein, x is a distance from a leading edge to a trailing edge along a chord line of the airfoil, c is a length of the airfoil in chord direction, yint is a distance between the chord line and a respective intrados surface and yext is a distance between the chord line and a respective extrados surface. The airfoils are usually further characterized by associated predetermined maximum thickness to chord ratios, as well as by leading edge radiuses r/c of corresponding leading edge circles and their center positions x/c and yint/c or yext/c.
The documents U.S. Pat. No. 5,957,662 A and U.S. Pat. No. 6,315,522 B1 describe such airfoils and illustrate exemplary tables of values that comprise values for predetermined intrados coordinate value pairs x/c, yint/c and predetermined extrados coordinate value pairs x/c, yext/c. More specifically, the document U.S. Pat. No. 5,957,662 A describes an airfoil with a maximum thickness to chord ratio of 8%, a leading edge radius r/c=0.00844 and corresponding leading edge circle center positions x/c=0.00842 and yext/c=0.00064. The document U.S. Pat. No. 6,315,522 B1 describes an airfoil with a maximum thickness to chord ratio of 10%, a leading edge radius r/c=0.0096 and corresponding leading edge circle center positions x/c=0.0097 and yint/c=−0.0018.
Furthermore, the document U.S. Pat. No. 6,361,279 B1 describes airfoils with maximum thickness to chord ratios of 12% (Table 3) and 9% (Table 5). Nevertheless, for these airfoils no leading edge radiuses r/c of corresponding leading edge circles and their center positions x/c and yint/c or yext/c are indicated. Instead, maximum camber positions and ratios of maximal camber to maximal thickness are used for further characterizing these airfoils.
However, these airfoils only provide for a restricted maximum lift capacity and a comparatively high aerodynamic drag. Furthermore, they only provide for restricted hover and forward flight performances.